confused about HID1 bits and G5
cfriesen at nortelnetworks.com
Thu Apr 29 23:54:06 EST 2004
Benjamin Herrenschmidt wrote:
>>It appears that we're relying on the firmware to set up a lot of the bits in this register--is there
>>any reason we aren't forcing particular values?
> Forcing values in HIDs is BAD. The firmware may set/clear bits to work
> around specific CPU or north bridge bugs for example. That's why I need
> to change the code that force-clear HID4/5 one of these days too and
> instead just clear the bits I want to be cleared.
I'm just thinking of stuff that should really be set, like enabling the icache or the branch history
table. Do we really want to rely on firmware to do that? 
Currently there are a bunch of bits in HID1 that are not specifically set in the linux code. I
think they should be set, but I have no way of actually checking the value since I'm running in
32-bit mode. 
1. We've seen at least one firmware that didn't do this for some 74xx hardware. Drove us nuts
trying to figure out why performance wasn't meeting projections.
2. I'm trying to get a 64-bit toolchain built, but the gcc doesn't build when I follow the
instructions on linuxppc64.org.
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